Trimtab

I read in Model Airplane News, "Ask Chris", about aluminum engine mounts for four stroke engines as the recommended type. I recently purchased a "Great Planes Giant Adjustable Engine Mount" (GPMG 1101) - described as made of "nylon" - for my new OS 120. Is this Nylon mount the same as a "fiber-filled composite engine mount" (term used in the article) which was not recommended by the author Chris?

I thought (guessed) an aluminum mount would transmit damaging vibrations simply because it is metal and therefore rigid. The giant scale model I'm building is the Arado 96B designed by David Andersen. I bought his plans and I'm modifying a DynaFlite Chipmunk kit to look like the Arado. The wingspan, fuselage, etc. are very close in size and their profiles are similar.

I would enjoy hearing from any of you folks out there with your experiences. I wrote to Model Airplane News asking if "nylon" was the same as "fiber-filled composite" and received a form letter type answer from their automatic response system. That was very frustrating especially when they encourage e-mail. My guess is it's probably a way of counting readership response for their advertising statistics.

da Rock

Any of the readily available engine mounts are fine. Companies like Great Planes didn't get their huge customer base selling weak motor mounts. Only thing you have to do is make sure to use an adequate size mount for your engine. If the recommended size on the mount covers your engine, it'll do the job. It is a good idea for 4strokes to make sure your engine size is not the largest engine size for the mount, but that's just extra caution. If you can't find a mount like that, don't sweat it.

I read that too and figured he'd just run out of things to fill out the column space. There is a brand of 4stroke (or maybe two) that's known to be shakers, and the advice probably is good for them, but he should have qualified that. However, as a magazine writer he would not have done that.

And a way to get a list of active email addresses. Bet you see an unsolicited advertisement or two sometime in the future.

Trimtab

Thanks for your response. The mount I have is for 1.20 - 1.80 size four stroke engines so it's well within the "shoe size". I wish these articles would use common terms to describe non-metal materials. Is nylon the same as "fiber-filled composite", a term he used in the article? Imagine describing a motor mount as being made of "metal" without stating what kind.

Charlie P.

I would say yes. "Nylon" is easier than saying a "silicate reenforced suspension within a synthetic polyamide resin matrix" - aka Glass-filled Nylon. Some are solid Nylon, some have fiberglass fibers in the cast for added strength. Some have nylon fibers within a nylon casing.

Think of this: if the motor mount doesn't break from whatever stress caused the failure; what else will? Many motor mounts are designed to fracture and save more costly or labor intensive replacement components like firewalls, casings, shafts and bearings.

Trimtab

The article spoke about how a "fiber-filled composite" mount transmits more damaging stress and vibration toward the aircraft structure in larger size (giant) models (above sixty size), especially with four-stroke engines, whereas an aluminum mount transmits less. He wasn't concerned about either of the mounts snapping or breaking away nor did he mention the benefits of an engine breaking away. It was more about reducing structural stress with an aluminum mount to avoid possible damage to the aircraft.

da Rock

It would be greatly interesting to find out why he thinks aluminum transmits less shock than a material that appears to be less rigid.

Doesn't it appear to you that solid metal would be more apt to transmit shock than a plastic material? It does to me.

Trimtab

Yes. Makes sense. This is exactly why I decided to send an e-mail question to them and subsequently received their automatic public relations response. I wonder if anyone knows how this guy Chris can be reached.

RICMOD5634

I have used the composites, aluminum/direct to fire wall and aluminum with rubber bushings. I don't see any difference in vibration, if the engine is tuned right. I read the same article and couldn't agree with it. Any solif is going to transmit a curtain amount of vibration and what its made of isn't going to matter,JMHO. Tune to smooth running and be done with it.
Ricmod

Trimtab

Thanks RICMOD.

There's a substantial difference in price. Around eight bucks for a Great Planes nylon mount and mid-thirtites for a Dubro aluminum mount. Most of the articles in Model Airplane News are nothing but product promotions anyway, pretending to be informational. The magazine ads have grown and the articles seem to be shorter and predictable. Most airplane articles have "flys like it's on rails" or "flys like a trainer" built in even if the airplane looks like a high-drag weight lifting device.

majortom-RCU

My Feedback: (40)

If the 'aluminum' mount is the Dubro soft mount with the rubber bushings, then without question that will transmit less vibration compared to a nylon or composite mount. It will also be considerably heavier. I was trained in my younger days to favor the Dubro soft mount, and must concede they are quieter. As far as shaking the model, especially around idle rpms, the model still shakes. But the vibration at higher rpms and the high frequency vibrations at any rpm are less of a problem with the Dubro soft mount.

However, as a practical matter, it is no big deal. I haven't used a soft mount on my two-strokes (gas or glow) in the last few years, and have experienced no vibration disasters or even noticeably degraded servo slop, which is perhaps the most serious consequence of vibration. That and things rattling loose, screws backing out, stuff falling off, etc. I do like the Hyde soft mounts for my YS installations, which are about the only four-stroke I use anymore, but these are not cheap (and neither are the Dubros). If you want an absolutely first class installation, Hyde is the way to go. Dubro soft mount maybe comes next if it's a four-stroke. For two-stroke, or to save lots of weight and or money, GP nylon works great. The Dave Brown glass-filled is also a very serviceable, lightweight, inexpensive product.

Trimtab

As mentioned earlier, I have the GP nylon for my OS 120 four stroke. Received Model Airplane News in the mail shortly after I purchased the GP mount. Read the article and then put my project on hold. Thanks to you and to all! Now I can continue building.

andrew66

I dont even look at that mag anymore (or too many others for that matter) i find its got about the same percentage of BS as the newspapers. they dont care about the product, all they care is which mfg can pay them the most for running an ad. and that mfg is the one with all the good reviews.
for reading and info purposes, i stick to this site. you tend to get many resopnses (most of which arent biased), there's pictures to look at, and videos. try and get that out of a crappy mag.....oh yeah....its also free

Trimtab

I agree. I will not be renewing my subscription. I also subscribe to Fly RC and I may not continue with that magazine either.

Funny thing and I have it tucked away. Model Airplane News had an issue which celebrated 100 years of RC modeling. Now figure that one out. Marconi sent the first message from the U.S. to the U.K. in 1903 from Wellfleet on Cape Cod. . . . 103 years ago.

andrew66

cool! i know that model airplane news was decent (aside from their biased reviews) when i was alot younger, i had interest in the hobby (never persued it though) and a guy from one of the clubs gave me his old issues of model airplane news. it at least included building techniques, a KIT review and all that great stuff that it is lacking today.